1. Field of the Invention
This invention relates to feedback systems, and more particularly to apparatuses, systems and methods for estimating particulate production from diesel engines.
2. Description of the Related Art
Environmental concerns have motivated the implementation of emission requirements for internal combustion engines throughout much of the world. Governmental agencies, such as the Environmental Protection Agency (“EPA”) in the United States, carefully monitor the emission quality of engines and set acceptable emission standards, to which all engines must comply. Generally, emission requirements vary according to engine type. Emission tests for compression-ignition or diesel engines typically monitor the release of diesel particulate matter (PM), nitrogen oxides (NOx), and unburned hydrocarbons (HC). A critical emission of gasoline or other stoichiometric engines is carbon monoxide (CO). Catalytic converters have been implemented in exhaust gas after- treatment systems for spark-ignition engines, eliminating many of the pollutants present in exhaust gas, though historically such aftertreatment systems have not been added to diesel engines. However, to remove diesel particulate matter, typically a diesel particulate filter, herein referred to as a filter, must be installed downstream from a catalytic converter or in conjunction with a catalytic converter.
A common filter comprises a porous ceramic matrix with parallel passageways through which exhaust gas passes. Particulate matter accumulates on the surface of the filter, creating a buildup that must eventually be removed to prevent obstruction of the exhaust gas flow. Common forms of particulate matter are ash and soot. Ash, typically a residue of burnt engine oil, is substantially incombustible and builds slowly within the filter. Soot, chiefly composed of carbon, which is refractory and not easily wiped away, can be oxidized and driven off of the filter in a process called regeneration. In most applications soot accumulates much faster than ash, to the extent that an estimate of the rate of soot accumulation is substantially equivalent to an estimate of the rate of total particulate accumulation.
Various conditions, including, but not limited to, engine operating conditions, mileage, driving style, terrain, etc., affect the rate at which particulate matter accumulates within a diesel particulate filter.
Accumulation of particulate matter typically causes backpressure within the exhaust system that can impair engine performance. Particulate matter, in general, oxidizes in the presence of NO2 at modest temperatures, or in the presence of oxygen at higher temperatures. Excessive soot buildup on the filter can precipitate uncontrolled regeneration of a particulate filter, or, in other words, cause rapid oxidation rates resulting in higher than designed temperatures within the filter. Recovery can be an expensive process.
To prevent potentially hazardous situations, it is desirable to oxidize accumulated particulate matter in a controlled regeneration process before it builds to excessive levels. Partial regeneration can contribute to irregular distribution of particulate matter across the substrate of a particulate filter.
Controlled regeneration traditionally has been initiated at set intervals, such as distance traveled or time passed, but that has proven to be ineffective. Regenerating a particulate filter with little or no particulate buildup lessens the fuel economy of the engine and unnecessarily exposes the particulate filter to destructive temperature cycles, and if particulate matter accumulates significantly before the next regeneration, backpressure from blockage of the exhaust flow can negatively affect engine performance. In addition, regeneration (intentional or unintentional) of a particulate filter containing large quantities of particulate buildup can become uncontrolled and potentially cause filter failure or the like. Consequently, many particulate filters regenerated on a set interval must be replaced frequently to maintain the integrity of an exhaust gas after-treatment system.
Recently, attempts have been made to estimate the amount of particulate matter accumulated in a particulate filter in order to respond more efficiently to actual particulate buildup.
In one method, the backpressure measured across a particulate filter by a differential pressure sensor or algorithm is used to estimate diesel particulate matter accumulation. The soot in the particulate filter may be burned off during regeneration to reduce backpressure in response to a differential pressure-based estimate of the amount of particulate accumulation.
In many cases, however, differential pressure alone is an unsatisfactory gauge of actual particulate accumulation due to unaccounted-for variations in engine operating conditions, sensor noise-to-measurement levels, exhaust flow estimate errors, reduced reliability at low exhaust flows, and unevenly-distributed particulate accumulation.
Other methods apart from differential pressure sensors have been developed to predict particulate accumulation, some of these comprising estimation or prediction models relating to known physical-chemical characteristics of the system and empirical data relating to engine operating conditions, mileage, driving style, terrain, and other factors. Existing models have been unsatisfactory in several respects, however, including poorly estimating particulate matter output, especially over time. Further, many empirical matches of particularized data sets end up with nonsensical coefficients contributing to the model; for example, a relationship between an operating parameter and the engine soot output might be reversed from the theoretical understanding. These effects reduce the ability to use a model in a broad set of applications
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for estimating or predicting particulate output from a diesel engine. Beneficially, such an apparatus, system, and method would contribute to effective and timely regeneration of a diesel particulate filter based on a more accurate estimate of soot accumulation, increasing the fuel economy of the vehicle, extending the life expectancy of the particulate filter, and increasing the overall efficiency of the engine.